My advice is to do everything until you've replaced most of your gear. In the first evening of outland, I doubled the hps on my team.

Make sure you have everything on free for all loot.

If you're using keyclone, make sure you can switch leaders easily. I'm basically just doing the collect quests 4 times. I switch leaders every time someone fills up.

You really should be able to take things down with little more than a triple mind blast, so the collects should go decently fast. With a 4 man team, I was getting about 200 xp per kill. Not terribly fast, but decent considering how fast I could put them down.

Anyway, at least for hellfire, you should do them to pick up the gear. Going from old gear to outland gear is the biggest jump you'll see until you start replacing things with epics.